01-14-2015, 12:14 PM
In circuit is fine, these are low values and do not depend much on stuff around them.
The voltage should by itself be negative as you measure from the Chassis to the centertap (where the bias comes from) which is negative. If you draw 30mA you have roughly -10 V. Then the tube will develop its own internal bias which will detract from that value but it can be still negative.
Or you cold change the tube and see if it improves performance: in circuit check is alwys the ultimate proof.
Same goes for other tubes.
The voltage should by itself be negative as you measure from the Chassis to the centertap (where the bias comes from) which is negative. If you draw 30mA you have roughly -10 V. Then the tube will develop its own internal bias which will detract from that value but it can be still negative.
Or you cold change the tube and see if it improves performance: in circuit check is alwys the ultimate proof.
Same goes for other tubes.
